Cellulose nanomaterials, such as cellulose nanocrystals (CNC), have unique mechanical and optical properties for a variety of applications. However, most cellulose is naturally embedded in the cell walls of plant lignocellulosic biomass with hemicelluloses and lignin in a hierarchical structure. Efficient extraction or production of cellulose nanomaterials from plant biomass is critical to successful commercial application. The strong acid hydrolysis approach for CNC production is a dominant process today. However, the focus has been on using mineral acids for acid hydrolysis. For example, hydrochloric acid, phosphoric acid, and sulfuric acid have all been used. Unfortunately, the isolated cellulose solids produced by strong acid hydrolysis generally suffer from poor thermal stabilities.
Cellulose nanofibrils (CNF), another kind of cellulose nanomaterial has attracted great attention in recent years for its good mechanical and optical properties. CNF can be produced simply through mechanical fibrillation. The breakdown of the cell wall to the nanofibril level is very energy intensive, which is a significant barrier for commercial CNF production. Chemical pretreatments can reduce this energy consumption. For example, alkaline pretreatment has been applied to separate the structural linkage between lignin and carbohydrate in the cell wall. TEMPO-mediated oxidation has also been used. However, TEMPO is a very expensive chemical and the technique for the recovery of TEMPO still needs to be developed. Furthermore, other chemicals as oxidants used in TEMPO-oxidation, such as NaClO and NaBr, cannot be recovered. In addition, CNF from TEMPO suffers from poor thermal stability for composite applications.